1. Field of the Invention
The present invention relates to a sewing machine, and more particularly to a sewing machine with an adjusting structure capable of controlling a swing center of a swing arm.
2. Description of the Prior Art
In the existing sewing machines, there are many mechanisms used to convert circular motion into linear reciprocating motion, therefore, the control of the travel of the presser feet has great influence on sewing quality. Different presser feet are designed to meet different sewing needs, which require the presser foot to have different travels, for example: when buttons are sewed, the presser foot should be specially designed in such a manner that one end of the presser foot is fixed on one end of the presser foot shaft, and the structure of the presser foot which presses the cloth can move along with the cloth. The corresponding total travel of the presser foot, as shown in FIG. 1, includes a first travel X1 starting from a start point X11 and ending at an end point X12 along the long side of the button hole, a second travel Y1 in the horizontal direction starting from a start point Y12 and ending at an end point Y22, a third travel X2 starting at a start point X21 and ending at an end point X 22, and a fourth travel Y2 starting at a start point Y21 and ending at an end point Y22. When the presser foot is located at the start point X11 of the first travel X1, the first sensing electrode of the travel sensor in the sewing machine will be turned on to make the sewing machine sew the long side of the button hole which starts from the start point X11 and ends at the end point of the first travel X1. After moving to a position where the second sensing electrode is turned on, the presser foot will start moving horizontally along with the cloth from the start point Y21 of the fourth travel Y2 to the end point Y22 and then directly turns to the start point X21 of the third travel X2 for performing the sewing operation along the third travel X2 and finally turns to the start point Y21 of the fourth travel Y2 for performing the sewing operation along the fourth travel until reaching the start point X11 of the first travel X1.
After the sewing machine is used for a period of time, some parts will become loose, hence, the positions where first and the second sensing electrodes are turned on are often different from the correct positions of the presser foot, which will produce a defective button hole, for example, as shown in FIG. 1-1, the two long sides of the button hole are different in length.
To solve the above problem, the positions where the first and the sensing electrodes of the travel sensing apparatus are turned on and the positions of the presser foot are designed to be adjusted, so that the start point of the respective travels of the presser foot can be controlled. However, since the corresponding adjusting structure is in the form of a cam, in the principle of mechanical designing, it is known that the cam may normally lead to non-single-direction displacement during the adjustment, in other words, when the displacement in the horizontal direction is needed to be adjusted, the displacement in the horizontal direction will be caused synchronously, thus leading to unneeded displacement, so that the travel of the presser foot is thus quite uncertain.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.